This application claims priority to German patent application number 102 10 332.1 filed on Mar. 8, 2002, which is incorporated herein by reference.
1. Field of the Invention
The invention concerns a contraction unit with a contraction tube that extends between two spaced head pieces and that contracts in length when pressure is built up on the inside.
2. Description of the Prior Art
Such contraction units are known from, e.g., the brochure xe2x80x9cFluidic Musclexe2x80x9d published by the applicant, EP 0161750 B1, DE 29906626 U, DE 29908008 U, or DE 20112633 U. These units can be used for very precise positioning with a simple and low wear and tear design and at relatively low costs. Very high positioning forces can be achieved.
In principle, for exact positioning, some type of position sensor or location sensor is required for actuators. In connection with position cylinders, a plurality of such position sensors and sensor devices are known, which work according to a wide range of measurement principles. However, these are absolutely unsuitable or only poorly suitable for contraction units of the previously mentioned type.
One problem of the present invention is to create a position sensor device that is well suited for such contraction units and that can realize higher precision easily and cost-effectively.
This problem is solved according to the invention by a contraction unit with a position sensor device with the features of claim 1.
More specifically, the advantage of the solution according to the invention is that an elastic measurement object can be realized very easily between the head pieces or in or on the wall of the contraction tube and can detect expansion with the help of an expansion measurement device, wherein the expansion of the measurement object is a measure for the distance between the head pieces of the contraction unit, i.e., for their position. Because both the expansion measurement device and also the elastic measurement object are arranged or integrated within the contraction tube or in its wall, a compact contraction unit is produced, whose position sensor device requires no additional outer elements which could cause mechanical damage or malfunction. One of the principle advantages of such contraction units, the complete seal and thus the low consumption of operating fluid, is not adversely affected by the position sensor device.
The measures listed in the subordinate claims permit advantageous refinements and improvements of the contraction unit indicated in claim 1.
In a first advantageous configuration, the measurement object is a stretched strand made of an electrically conductive plastic or rubber material stretched between the head pieces, wherein the expansion measurement device is designed as a resistance measurement device for the electrical resistance of the stretched strand. Such a solution can be realized especially simply and cost-effectively and is practically insusceptible to malfunction.
Thus, the two end regions of the stretched strand can be connected directly to the resistance measurement device or to the two head pieces, so that the resistance between the two head pieces is measured. Alternatively, the stretched strand can also consist of two parallel partial strands with first regions that are connected electrically to each other and second end regions that are connected to the resistance measurement device. The second configuration has the advantage that the electrical measurement device only has to be connected to one of the two head pieces.
In an alternative configuration, the measurement object can also be designed as a measurement strand and can consist of an electrically conductive plastic or rubber material, which is arranged in or on the wall of the contraction tube. The expansion measurement device is formed as a resistance measurement device for the measurement strand. Thus, the measurement strand can be preferably integrated in the wall of the contraction tube.
The plastic or rubber material of the measurement object is preferably mixed with electrically conductive particles or fibers for generating the electrical conductivity. If the measurement strand is integrated into the wall of the contraction tube, these particles can also be arranged directly in regions, preferably elongated regions, of the contraction tube wall.
In another alternative configuration, the measurement object is a stretched strand made of a plastic or rubber material mixed with ferromagnetic particles or fibers stretched between the head pieces. The strand is at least partially overwrapped by a coil, wherein the expansion measurement device is designed as an inductance, frequency, or resonance measurement device and the coil forms a part of this device. When the contraction unit contracts, the ferromagnetic portion in the coil increases, so that the inductance of the coil changes as a function of the position of one head piece relative to the other head piece. If this coil forms a part of a resonant circuit, then this action changes the frequency or resonance frequency. Thus, the coil advantageously forms a resonance resonant circuit together with the capacitor.
In another alternative configuration, the expansion measurement device has at least one expansion sensor, which is arranged on the wall of the contraction tube or on a stretched strand in tension between the head pieces. When the tube contracts, the expansion of the wall or the stretched strand changes, so that the position can also be detected indirectly. Preferably, the expansion sensor is formed as a wire strain gauge or a magneto-elastic sensor.